Technical Abstract:
Despite much research on the casein micelles, the colloidal calcium-phosphate complexes of skim milk, the molecular interactions involved in the casein micelles remain elusive. We investigate casein precipitated by pressurized carbon dioxide (CO2 casein) to elucidate the mechanism of the formation of casein aggregates using AFM techniques in tapping mode. Native casein micelles prepared from skim milk and calcium caseinate derived from acid casein precipitation were also studied in comparison. Images showed significant difference in average particle sizes and distribution among various caseins. Experiments at various concentrations of NaCl, NH4HCO3 and NaiH(3-i)PO4 were also conducted to examine pH and ionic effects on the casein aggregates. Results showed that inter-molecular protein-protein interactions on two distinctive levels may be the driving forces for the formation of casein aggregates in casein precipitated by pressurized CO2. This work not only provides insights on the nature of molecular forces attributable to casein aggregates formed by pressurized CO2 but sheds light on the role of casein in the formation and stabilization of the casein micelles.